1. Field of Invention
The invention relates to a method and an article of manufacture that employs a high temperature optical transducer to transform light signals arising from illumination during the combustion cycle into discrete electronic signals, and thus accomplish the acquisition of control variables for closed-loop control of combustion power systems.
2. Description of Related Art
The invention relates to a high-temperature optical transducer to accomplish the acquisition of input variables for closed-loop control of combustion systems. Signals from an optical transducer element can be used in a feedback loop to improve engine performance in terms of cyclic stability, knock, combustion timing, and in-cylinder temperature/NO.sub.x control. Optical signals may be used to recognize events such as the ignition spark, the start of combustion, and the end of combustion. Engine roughness, misfires, and knocking can be detected by high-speed, real-time optical methods. Signals from optical transducers may be used in a statistical fashion to control engine roughness and cyclic stability. By resolving specific colors in the flame, optical sensors may be used to determine the temperature and the emission production in the combustion chamber.
U.S. Pat. No. 3,978,720 discloses a device for detecting combustion within a cylinder of an internal combustion engine by sensing the visible and/or infra-red radiation emitted during combustion by means of a quartz window in the cylinder wall or head, a fiber-optic light guide and a phototransistor.
Optical combustion sensors can be used to acquire time-resolved combustion process parameters in a cyclical sequence such as the internal combustion engine. Crank angle and time delay between the initiation of spark and the start of combustion, maximum pressure in combustion and end of combustion can be determined from the optical signal. In a similar fashion, the time-domain parameters can be extracted in a compression ignition process by optical measurement. U.S. Pat. No. 4,381,748 discloses a method for regulating the combustion of operating mixtures in the combustion chambers of internal combustion engines. The intensity of the light resulting from combustion is detected and evaluated over the course of combustion; time-domain reference control variables such as turning points of the light intensity curve, the maximum of the light intensity curve, and the point where the light intensity curve increases are derived. The control signals obtained are an expression of the combustion chamber status in terms of pressure and temperature. U.S. Pat. No. 4,919,099 discloses a method of monitoring combustion within a cylinder of a reciprocating piston internal combustion engine by deriving first and second electrical signals representative of light intensity within the cylinder by means of optical transducers of spaced spectral response at common or closely adjacent locations and establishing a signal representing the ratio of the first and second electrical signals used as a control parameter for an engine control system.
U.S. Pat. No. 4,930,478 discloses an internal combustion engine having a luminosity probe and an arrangement for adjusting the running parameters of the engine to obtain the desired luminosity. Also disclosed in U.S. Pat. No. 4,930,478 is an arrangement for maintaining uniformity from cycle to cycle in a given combustion chamber and uniformity of combustion in the combustion chambers of a multi-chamber engine. U.S. Pat. No. 5,113,828 discloses an extension of the forgoing based on particular gain-independent parameters of the luminosity signal. Gain-independent (i.e. time-domain rather than intensity) luminosity parameters can be used to obtain uniform combustion conditions from cycle to cycle in a given combustion chamber and uniform combustion in the combustion chambers of multi-chamber engine. U.S. Pat. No. 5,103,789 also extends on the forgoing and discloses an arrangement for measuring and controlling combustion phasing based on the location of particular gain-independent parameters of the luminosity signal.
Time resolved optical signals may be used to determine the occurrence of a misfire event in an internal combustion engine. U.S. Pat. No. 5,125,381 discloses such an engine misfire detector comprised of an optoelectric sensor for monitoring light produced by combustion inside a cylinder. The sensor is connected to a variable gain amplifier; and the output of the gain control circuit is compared to a threshold using a comparator to provide a misfire detection signal.
Lean burn operation of an internal combustion engine reduces the combustion temperature, and thus the production of NO.sub.x, but results in an increase in the instability of the combustion and an increase in knocking. Optical signals from the combustion event can be used to determine the occurrence of predetonation and the engine operating parameters. Knocking can be detected by a differential analysis of the optical signal before the onset of knock, whereas pressure transducers can only detect knock after it occurs. U.S. Pat. No. 4,358,952 discloses a sensor system to detect detonations in an internal combustion engine constructed as a unit that may be threadedly (sic) engaged with the combustion chamber wall. U.S. Pat. No. 4,381,748 discloses that detection of light emission is well suited to early recognition of knocking combustion and its consequent prevention by means of a suitable regulatory intervention. U.S. Pat. No. 4,919,099 discloses the use of detectable and recognizable differences in the light intensity signal to determine the occurrence of knock in the combustion process.
An optical transducer can be utilized for the real time determination of the excess air ratio (.lambda.) or the fuel/air equivalence ratio (.phi.) by the acquisition of spectrally resolved intensity information that is correlated to the chemiluminescence of combustion product radicals. Use of this information can be used to form a closed-loop control algorithm where the internal combustion engine can be operated in a lean condition near the knock limit, reducing the actual level of pollutants emitted, or the air-fuel ratio can be maintained in a narrow range near the stoichiometric air-fuel ratio where so-called "three-way" catalytic converters operate most efficiently. The present oxygen sensor used in automobiles is comprised of an electrochemical cell in the exhaust stream. There is no proportional response in this device (it operates in "on-off" mode) and the control system is typically open-loop in nature.
U.S. Pat. No. 4,358,952 discloses an embodiment of this nature with the fundamental features of at least one filter disc disposed in front of the detector so that selective processing of the received optical signals is possible; if several individual filters having different selectivity are used, differentiation of various radiation bands for example HC, CO, OH is achieved.
Ohyama, et al. [1990] report on an internal combustion control system that utilizes a 1 mm diameter fiber optic probe which extends through the center of a spark plug. The CH and C.sub.2 radicals are associated with the 431 nm and 517 nm wavelengths of light and can be correlated to the excess air ratio (.lambda.). In this work, predetonation (knocking) was detectable by the analysis of pressure and optical data. Sohma, et al. [1991] report that the ratio between 431 nm and 517 nm wavelength flame emission can be used to calculate the excess air ratio and that two color pyrometry can be used to estimate the flame temperature in a combustion chamber at a data collection rate of 50 kHz. These results indicate that the air/fuel mixture can be determined accurately for .lambda.=0.8 to 1.5. Sohma et al. [1991] found that the flame temperature is well correlated to engine knocking. The optical sensor utilized in these two reports was a photomultiplier tube. This type of detector is not practical for a production engine control system due to the high voltages required and the relatively high cost of this kind of instrumentation. These forgoing results are disclosed in U.S. Pat. Nos. 4,444,169, 5,186,146, and Re. 34,211.
U.S. Pat. Nos. 5,067,463 and 5,099,683 disclose that an internal combustion engine having a luminosity detector and an arrangement for measuring certain operating and running parameters such as peak heat release rate in the combustion chamber, NO.sub.x emissions and air/fuel ratio is provided. An arrangement is also disclosed wherein the engine's adjustable parameters can be varied in response to the luminosity signal or in response to other measured operating parameters so as to provide better running of the engine and or reduce cycle to cycle variations.
The optical signal due to a combustion process may be used to determine flame temperature. U.S. Pat. Nos. 4,444,169 and 5,186,146 disclose that flame temperature is calculated using the ratio of electrical signal outputs from photoelectric conversion elements based on an optical signal obtained from thermal radiation having wavelengths including none of the wavelengths of an optical signal obtained from radical emission. U.S. Pat. No. 5,467,185 discloses that respective SiC (silicon carbide) photodiode sensors are used to measure flame temperature at each cylinder of an internal combustion engine, and information generated by the SiC photodiode sensors is used to control the fuel injection in a feedback loop to adjust individual cylinder flame temperature and combustion parameters.
U.S. Pat. No. 4,468,949 discloses an apparatus for detecting operating characteristics of an internal combustion engine. It has an optical sensor whose output signal is delivered to an amplifier with a variable transmission behavior. As a result, it is possible to have either a stepped or a continuous adaptation of the sensor sensitivity to various operational points of the engine. It is particularly proposed that the amplification for the measurement signal be selected to be high in the case of an optoelectronic combustion chamber observation in a low load range, while it is selected to be low in a high load range, so that relatively equalized measurement results are available.
U.S. Pat. No. 4,940,033 discloses an internal combustion engine having a luminosity probe and an arrangement for measuring certain parameters such as combustion chamber pressure, heat release and the like by measuring luminosity in the chamber and adjusting the running parameters of the engine to obtain the desired luminosity. Also disclosed is an arrangement for maintaining uniformity from cycle to cycle in a given combustion chamber and uniformity combustion in the combustion chambers of a multi-cylinder engine.
U.S. Pat. No. 4,891,970 discloses a luminosity and temperature detector for an internal combustion engine and method for measuring luminosity including a light probe and photodiode that receives the light transmitted from the light probe. The photodiode is designed, constructed, and biased to operate within the zero temperature coefficient portion of its range for the wavelengths being measured. In addition, the dark current is measured when there is no luminosity due to combustion and this is subtracted from the other readings to obtain temperature compensation. Furthermore, the dark current measurement will indicate the temperature of the photodiode. The responsivity and dark current of a photodiode change with temperature. These disclosures do not appear to be correct in all details to one skilled in the art. In particular, while variations in dark current are a well-known measure of junction temperature, the "zero temperature coefficient portion" of a silicon photodiode's response curve has existance only over a limited temperature range and the subtraction of the dark current from the light-generated current in a photodiode will not result in an output signal that is independent of the temperature variations in operation.
The foregoing disclosures indicate that the characterization and active control of the combustion process using optical signals is technically feasible through many different forms and implementations, but the optical control systems with the hardware and apparatus used to date are prohibitively expensive. A device that has the following three attributes is required to implement the control methods disclosed above: 1) the device must be able to convert the optical signals due to the combustion event to electrical signals which can be transmitted to a control module, 2) the device must have a configuration and manufacture such that the employment of said device is practical for a production engine, and 3) the device must have a reasonably long operational lifetime in such a production engine.